Force AXPlatformNode to have the same unique id as the owning BA object.

This CL allows us to override the AXPlatformNode's GetFromUniqueId
method.  In BrowserAccessibilityComWin we implement this by using the
BrowserAccessibility GetFromUniqueId.

BUG=703369

Review-Url: https://codereview.chromium.org/2894673003
Cr-Commit-Position: refs/heads/master@{#473771}

content/browser/accessibility/browser_accessibility_com_win.cc

@@ -4105,6 +4105,12 @@ void BrowserAccessibilityComWin::Init(ui::AXPlatformNodeDelegate* delegate) {
   AXPlatformNodeBase::Init(delegate);
 }
 
+ui::AXPlatformNode* BrowserAccessibilityComWin::GetFromUniqueId(
+    int32_t unique_id) {
+  return ToBrowserAccessibilityComWin(
+      BrowserAccessibility::GetFromUniqueID(unique_id));
+}
+
 std::vector<base::string16> BrowserAccessibilityComWin::ComputeTextAttributes()
     const {
   std::vector<base::string16> attributes;

content/browser/accessibility/browser_accessibility_com_win.h

@@ -753,6 +753,7 @@ class __declspec(uuid("562072fe-3390-43b1-9e2c-dd4118f5ac79"))
   //
   void Destroy() override;
   void Init(ui::AXPlatformNodeDelegate* delegate) override;
+  AXPlatformNode* GetFromUniqueId(int32_t unique_id) override;
 
   // Returns the IA2 text attributes for this object.
   std::vector<base::string16> ComputeTextAttributes() const;

ui/accessibility/platform/ax_platform_node.h

@@ -50,7 +50,7 @@ class AX_EXPORT AXPlatformNode {
   AXPlatformNode();
   virtual ~AXPlatformNode();
 
-  AXPlatformNode* GetFromUniqueId(int32_t unique_id);
+  virtual AXPlatformNode* GetFromUniqueId(int32_t unique_id);
 
   int32_t unique_id_;
 };